This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. We will compare and contrast two microscopy techniques used to measure FRET in live cells. We will use ratiometric imaging by comparing ratios of intensities of the donor and acceptor fluorophores, versus Fluorescence Lifetime Imaging Microscopy (FLIM) which measures the change in lifetime of the donor fluorophore as it is quenched by the acceptor.